1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus. More specifically, the present invention relates to a small zoom lens and a compact imaging apparatus that is employed in such as a video camera or a digital still camera, which treats such as a fixed imaging element as an imaging element thereof.
2. Description of the Related Art
A demand is being made upon a digital camera for both a higher performance and a greater degree of miniaturization thereof. A similar demand is also being made upon a zoom lens that is employed as an imaging lens of the digital camera for both the higher performance and the greater degree of miniaturization thereof. With respect to the miniaturization aspect of the zoom lens, it is necessary to begin by shortening an overall length of the lens, i.e., a maximum distance from a lens surface that faces a photographic subject to an imaging site of the digital camera, when the lens is deployed for photographic use.
Improving the performance of the zoom lens will require that the zoom lens comprise a resolution that supports an imaging element comprising between five and 10 megapixels, at a minimum, across an entire zoom range thereof, if an application thereof to a high-end digital camera is to be contemplated.
A solid demand also exists for an increasingly wide angle and a greater degree of magnification of a photographic lens of the digital camera. A half field angle at a wide-angle end of 38 degrees or more is desirable in this regard. A half field angle of 38 degrees corresponds to a focal length of 28 mm when converted to an application upon a 35 mm silver halide film camera, i.e., a camera of a Leica variety, as an instance thereof. A demand for a magnification of at least 5× is also explicitly required, as always.
A technique is known of effecting a weight reduction in a camera that comprises the zoom lens by refracting an optical path by interposing a prism within an optical assembly of the zoom lens; refer to Japanese Patent Application Publication No. H8-248318 and Japanese Patent Application Publication No. 2000-131610 for particulars.
The zoom lens that is disclosed according to Japanese Patent Application Publication No. H8-248318 and Japanese Patent Application Publication No. 2000-131610 is optimized for use with a video camera. According to a specific embodiment thereof, the zoom lens thus disclosed is a large zoom lens, comprising a magnification of 8× or more, according to Japanese Patent Application Publication No. H8-248318, or a magnification of 11× or more, according to Japanese Patent Application Publication No. 2000-131610. The zoom lens thus disclosed, however, further comprises a half field angle of a wide angle end that is on the order of either 25 degrees, according to Japanese Patent Application Publication No. H8-248318, or 31 degrees, according to Japanese Patent Application Publication No. 2000-131610, and thus, cannot be considered suitable for facilitating the half field angle of 38 degrees or more that is demanded for use with digital cameras. In addition, according to the specific embodiment that is disclosed in Japanese Patent Application Publication No. H8-248318 and Japanese Patent Application Publication No. 2000-131610, a large distortion aberration, on the order of 8%, is present with respect to the wide angle end thereof, which is inadequate as a specification for use as a high performance specification zoom lens.